Seven journalists have been arrested by police investigating an alleged plot to overthrow the Turkish government.

They were among 10 people detained as part of an official inquiry into Ergenekon, an ultra-nationalist clandestine group accused of trying to launch a coup against the government headed by Recep Tayyip Erdogan.

Among those under arrest is Nedim Sener, named last year as an International Press Institute (IP) world press freedom hero. He works for the daily newspaper Milliyet.

Among the other journalists held after raids on their homes and offices were Ahmet Sik and four writers with the odaTV.com news website - Soner Yalçın, İklim Kaleli Bayraktar, Mümtaz İdil and Doğan Yurdakul.

Professor Yalçın Küçük, a writer who is a prominent critic of the governing party was also detained.

Dozens of Ergenekon suspects, including businessmen, retired military officers, journalists and academics, are currently in prison on terror and coup charges.

They are said to have been involved in a conspiracy in 2007 to create chaos in order to provoke a military coup.

IPI director Alison Bethel McKenzie said: "No journalist should face arrest, charges, imprisonment or any other form of harassment or intimidation for doing their job... We urge the authorities to release all of the journalists imprisoned because of their work.

"A flourishing, diverse, critical media is a cornerstone of any healthy democracy."

The Turkish Journalists Association says that 58 of the country's journalists have been imprisoned. A US state department spokesman, Philip Crowley, said last month that the US had "broad concerns about trends involving intimidation of journalists in Turkey."